The present invention relates in general to a method and apparatus for providing power to an automotive multimedia/personal computer system, and, more specifically, to a system for providing power to volatile ram during engine startup.
Power management is an important issue in portable computing devices. This is especially true in mobile vehicles which have a limited battery capacity and stringent current limitations. As microprocessor-based systems become more powerful by using larger microprocessors and using a greater number of peripheral devices, power requirements increase. In vehicles containing an internal combustion engine and an alternator, electric power generation may be sufficient to operate without much difficulty. In vehicles using other power plants or in an internal combustion engine vehicle with the engine shut off, significant limitations may be placed on current consumption(both normal operating current and quiescent current) of the multimedia/PC system.
Power requirements within the vehicle are typically at their highest when starting the vehicle. A starter motor can require the entire power generating capacity of the battery thereby causing battery voltage to drop below a minimum required voltage for safe operation of electrical devices (known as a brown out condition). During this peak load time, electrical devices which are active could be damaged or lose critical data stored in volatile random access memory (RAM) as a result of the drop in battery voltage. The loss of the critical data can force a device to become nonfunctional or have to spend extra time reconfiguring to allow proper functioning.
In the past, electrical devices have used other power sources, such as a secondary battery, to overcome the loss of main battery voltage during engine startup. As the battery voltage is reduced, the secondary battery keeps a minimum voltage supplied to the device to allow continued function and no loss of stored data. A problem with this is the extra secondary battery can be expensive and extra space is needed for the storage of the secondary battery within the vehicle.
Electrical devices must be able to respond very quickly to power loss. The devices must be able to protect and save any critical data within milliseconds before the engine actually starts cranking and battery voltage drops. Current technology is limited because most multimedia/PC based systems use processors not equipped to shut down quickly or deal with a sudden loss in battery voltage.
The present invention has the advantage of providing an efficient and safe method of shutting down an in vehicle computer based system during engine start up while preserving the contents of volatile random access memory.
In one aspect of the invention, a power management system for providing energy to volatile ram in a processor based electronic system is installed in a vehicle having an engine. The vehicle includes an engine crank signal for detecting a startup condition of the engine and a main electrical power source. The system includes a main processor board for performing information processing. The main processor board includes an input for the engine crank signal and the main processor board is coupled to, or contains, the volatile ram.
The power management system also includes a vehicle input/output processor board for performing real time processing of vehicle interfaces, user inputs, and overall power management of a plurality of peripheral devices. The input/output processor board is coupled to the main processor board and also includes an input for the engine crank signal.
The power management system further includes a primary voltage regulator for powering the main processor board. The primary voltage regulator generates a primary regulated output voltage in response to a primary input voltage. The primary voltage regulator is also coupled to the input/output processor board and the main electrical power source.
The power management system further includes a secondary voltage regulator coupled to the volatile ram to provide power at least during startup of the engine. The secondary voltage regulator generates a secondary regulated output voltage in response to a secondary input voltage and is coupled to the main electrical power source.
The primary voltage regulator provides the primary regulated output voltage as long as the primary input voltage is within a primary voltage range. The secondary voltage regulator provides the secondary regulated output voltage as long as the secondary input voltage is within a secondary voltage range which contains voltages lower then the primary voltage range so that it can power the ram when the main power source voltage drops during cranking.
The main processor board detects the engine crank signal and goes into a suspend mode in which predetermined devices controlled by the main processor board are shut down. As the predetermined devices are shut down, the main processor board stores a current state of all devices controlled by the main processor board into the volatile memory for recall after the engine is started and the main power source voltage recovers.